1. Field of the Invention
The present invention relates to a thin section preparing apparatus and a thin section preparing method, in which an embedded block having a biological sample embedded therein is sliced to prepare a thin section and the prepared thin section is carried to a subsequent process step as a step before a thin section sample is prepared for use in physicochemical experiment or microscopic observation.
2. Description of the Related Art
Heretofore, as one method of examining a biological sample taken out of a human body or a laboratory animal, such a method is known that a biological sample is sliced in an ultrathin section and applied to various stains, and then examined by microscopic observation. This examination method is mainly known as a technique that is adopted in conducting a toxicological examination or a histopathological examination, which is one of examinations prior to clinical trials in new drug development.
Generally, in conducting this examination, in order to slice a biological sample so as not to damage the form of soft tissue or cells, first, the biological sample is embedded in an embedding material such as paraffin in advance to form an embedded block. Then, this embedded block is sliced to have a thickness of about 2 to 5 micrometers, whereby a thin section is prepared. In this manner, even though an examination subject is soft tissue, the examination subject can be sliced in an ultrathin section without damaging the form.
Then, after the thin section is carried, it is fixed on a substrate such as a slide glass, whereby a thin section sample can be prepared. Generally, an operator observes the thin section sample under a microscope to conduct various examinations. In microscopic observation, because a wrinkle or a breakage in a thin section hampers observation, the preparation of a thin section with no wrinkle or breakage is demanded.
For example, in preclinical trials, an enormous number of thin sections prepared from hundreds of embedded blocks are sometimes used. On this account, an operator requires a huge number of man-hours to prepare thin sections. In order to reduce even a small amount of these man-hours, an attempt is made to automate a sequence of process steps of preparing a thin section to continuously prepare thin sections.
Particularly, in order to automatically and continuously slice an embedded block, it is necessary to automatically carry thin sections sliced by a cutter. To this end, for example, in a thin section preparing apparatus described in, for instance, JP-A-2007-178287, an endless belt is used as a carrying mechanism. This endless belt is wound between a roller arranged near a cutter along the nose direction almost in parallel with the nose of the cutter and a plurality of the other rollers arranged on the rear side of the roller, and the endless belt is configured to travel in the transport direction nearly vertical to the nose direction seen in plane.
According to this thin section preparing apparatus, while a thin section is being sliced off from an embedded block by the cutter, the sliced thin section can be passed onto the endless belt arranged near the cutter. Therefore, the embedded block is sliced by the cutter while the endless belt is traveling in the transport direction, whereby thin sections can be automatically carried to the subsequent process step as thin sections are prepared. As described above, since the prepared thin sections can be automatically carried, working efficiency can be improved. Thus, man-hours to be consumed in preparing thin sections can be reduced.
When the embedded block is repeatedly sliced by a cutter, the sharpness of the cutter is gradually degraded. In order to maintain the sharpness of the cutter as long as possible, such a method is generally known that a pull angle is provided to a cutter with respect to an embedded block for slicing. In addition, the provision of the pull angle to the cutter with respect to the embedded block means that the cutter is arranged in such a way that the nose direction intersects at an angle other than an angle vertical to an approaching and separating direction seen in plane in which the cutter and the embedded block approach and separate from each other for slicing the embedded block.
Therefore, preferably, the pull angle is provided to the cutter also in the apparatus before. However, it is necessary to carry sliced thin sections with the use of the endless belt, which might cause inconvenience. In other words, in passing a thin section onto the endless belt, a wrinkle or a breakage might occur in the thin section. The detail will be described below.
As shown in FIG. 11, in slicing off a thin section S from an embedded block B, the rate of travel is different between a portion P11 that has been sliced off by a cutter and placed on an endless belt 102 and a portion P12 that is not sliced off yet and remains in the embedded block B.
In other words, to the portion P11 placed on the endless belt 102, a block velocity vector V11 in approaching the cutter 101 and the embedded block B to each other along an approaching and separating direction L and a transport velocity vector V12 in moving the endless belt 102 along a transport direction M are applied. Thus, the rate of travel of the portion P11 placed on the endless belt 102 is a combined velocity vector V13 that is the combined vector of the block velocity vector V11 with the transport velocity vector V12. On the other hand, the rate of travel of the portion P12 remaining in the embedded block B is the block velocity vector V11 that is the rate of travel of the embedded block B.
Therefore, in order to automatically prepare the thin section S in the apparatus before, the portion P11 placed on the endless belt 102 and the portion P12 remaining in the embedded block B are being moved at different rates of travel (at the combined velocity vector V13 and at the block velocity vector V11) in a single thin section S. On this account, because a difference is caused between the rates of travel in a single thin section S, a wrinkle or a breakage occurs in the thin section S.